The present invention relates to an auto focus camera.
In the prior art, auto focus cameras with an optical distance-measuring apparatus having a light-emitting element and a light-receiving element for position detection are well known. For instance, Japanese Patent Laid-Open No. 60511/1985 discloses the following arrangement: An infrared beam of light operated via an infrared light beam source-driving circuit is applied to an object to be photographed via a single projection lens, reflected light thereof is caused to form an image on a PSD (positive sensitive diode) light-receiving element via a single light-receiving lens, and a distance to the object to be measured is calculated by an arithmetic processing circuit on the basis of that image-forming position, thereby automatically adjusting the focal length of a lens.
In addition, Japanese Patent Laid-Open No. 223734/1987 discloses the following arrangement: A plurality of light-emitting elements are juxtaposed, and, as a PSD light-receiving element, one having a large width corresponding to the respective light-emitting elements is used. Respective distances to objects to be measured are calculated by an arithmetic processing circuit to obtain an average value thereof, and the focal length of a photographic lens is automatically adjusted by this average value. With this distance-measuring apparatus, in order to make the width of the PSD light-receiving element as small as possible, one is used in which the plurality of light-emitting elements are juxtaposed perpendicularly to the lengthwise direction of a base line and has a PSD light-receiving element with a width expanded similarly in the perpendicular direction.
In both the first and second prior art arrangement described above, the results of distance measurement are obtained by calculation, so that there is the problem that it takes time in obtaining an in-focus condition. Moreover, if an addition and a subtraction are made with a correction value with respect a distance signal, the calculation becomes even more complicated. In addition, since a special arithmetic control circuit is required for obtaining an average value, the circuit configuration becomes complicated, so that high-speed processing becomes impossible.
Furthermore, in accordance with the above-described first prior art arrangement, if an attempt is made to photograph two object persons standing with an interval longer than a fixed one therebetween, there are cases where a focus zone is located between the two persons, and the background between the two persons is brought into focus, with the result that the objects are photographed in a blurred state, resulting in a so-called passing-through-the-middle phenomenon. In addition, since the closest object is brought into focus, there is a problem in that a remote object becomes out of focus, so that, for instance, it becomes impossible to portray a picture in a "flat" manner at the time of simultaneously shooting a near person and a far scene.
Therefore, to prevent this passing-through-the-middle phenomenon from occurring, there is an arrangement in which a camera is first directed toward one person, and the shutter release button is half pressed when an in-focus state is obtained, and with that state maintained, i.e., by locking the focussing position of the photographic lens, the shutter release button is then pressed after the two object persons are framed in a desired photographic zone. However, such an operation is complicated, and the photographer may make a mistake unless he is familiar with that operation.
Furthermore, in accordance with the above-described second prior art arrangement, a wide chip is required as the light-receiving element, and there is a problem in terms of cost, and, in order to prevent the occurrence of the passing-through-the-middle phenomenon concerning objects juxtaposed laterally, both the light-projecting and light-receiving elements must be arranged vertically, so that there are numerous problems.